Control device for audio reproducing systems including a cross-over network



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Oct. 7, 1958 CONTRO NORMAN INVENTORS R. THRESHER ERNEST H.F|DELLOWUnited States Patent 0 CONTROL DEVICE FOR AUDIO REPRODUCING SYSTEMSINCLUDING A CROSS-OVER NET- WORK Norman R. Thresher and Ernest H.Fidellow,

Our invention is an electronic device designed primarily for use inassociation with conventional audio reproducing equipment including asignal receiving system. and a system for converting said signal intoacoustical energy. Its primary object is. to so control the audio outputof the associated equipment as to automatically exclude speech from itsloudspeaker, admitting to audibility only the musical portions ofbroadcast programs or other signal sources.

To accomplish our purpose, the A.-F. signal is tapped off someconvenient point in the associated system and inserted into thecircuitry of our invention. From this input signal is developed acombination of D.-C. control voltages the net effective resultant ofwhich is characteristically different when developed from speech signalsthan when developed from music signals. If said circuitry determines theinserted A.-F. signal to be speech, it is intercepted at some point inthe audio system before it can be converted into acoustical energy; butif the determination be that the inserted signal be music, it ispermitted to complete its course unimpeded, to energize the loud speakervoice coil and become audible.

The development of the discriminating control voltages in our inventionis founded on the principle that, when a full spectrum of inserted audiofrequencies is divided at an appropriate frequency, the ratio ofupper-frequency energy to lower-frequency energy is greater in the caseof music signals than in the case of speech signals. Therefore, theenergy represented by the resulting ratio-differential may beeffectively applied to discriminate between speech and music signals,respectively.

Upon devision at an appropriate frequency-level, speech signals developan appreciably lower upper-frequency to lower-frequency energy-ratiothan do the great preponderance of music signals, when the latter aresubjected to a corresponding frequency-division, because r speechsignals are largely confined to the lower frequencies insofar asenergy-development is concerned; whereas music signals are comparativelyfuller in spectrum, containing fundamentals much higher in frequency andricher. in harmonic content. Thus, if 400 C. P. S. be taken as anappropriate reference frequency, the energy which speech develops in theband above 400 C. P. S. as compared with that developed in the bandbelow 400 C. P. S. is found to be unity or less, which is appreciablysmaller than the corresponding ratio in the case of a representativemusic signal.

Application of the general principle above stated may be convenientlyillustrated. If, by some appropriate means, a full A.-F. spectrum wereto be divided about some reference frequency, as 400 C. P. 8., so thatits lowerfrequency band were rectified to a positive DC. voltage, andthe upper-frequency band of the. same signal were simultaneouslyrectified to a negative D.-C. voltage; and if these two components wereto bemixed across a common load; a degree of" self-cancellation oftheoriginal signal would take place. A D.-C. potentialwould result, bearinga polarity and magnitude each dependingon the :fxat relative magnitudesof the two rectified components, which in turn are dependent upon thefrequency-content of the A.-F. spectrum originally inserted.

The foregoing application of the general principle is utilized in thecircuitry of one manifestation of our. invention, as will be detailed inthe disclosure to follow. Therein, D.-C. voltages are developed whosenet effective result is to convert inserted speech signals into alargely positive D.-C. control voltage, whereas music signals areconverted into an exclusively negative D.-C. control voltage. Saiddiscriminatory control voltage is applied to dietate the acousticaloutput of the associated equipment accordingly.

Furtherobjects of our invention include a reverse operation, whereinmusic signals are suppressed and speech signals alone are admitted toaudibility. Such an arrangement is practical in certain applications, aswhere our system is employed by advertising agencies for monitoring thecommercial announcements of their accounts, the receiver being mutedduring intervening musical selections.

A further object of our invention is to provide a system whereby musicalportions of programs are reproduced at normal volume-levels, whereas thespeech portions are pre-adjustably subdued in volume-level, as for usesin lounges, restaurants, or wherever background music may be desiredwithout total suppression of the speech portions of programs. Thisapplication may become important as civilian defense activities shouldincrease. Further, it affords a means whereby announcements may bemonitored for news items, musical titles, and bulletins of possibleimport to the listeners, yet without obtrusion of the speech signalsupon those who choose to ignore them. The accent may be reversed,emphasizing the speech portions while subduing the musical portions ofspeciallyprepared program material, as for use in shopping centers wherestress on commercial announcements is desired.

An incidental function which our invention is capable of performing isto distinguish between a signal lying within an upper-frequency band andone falling within a lower-frequency band as means for variouslyoperating a relay or similar device to respond accordingly. Alowpitchedbuzzer and a high-pitched bell at the rear and front door, respectively,of a dwelling might also be made to serve as signals to illuminate theparticular entrance area at whichthe caller is ringing. The applicationmay be directed to the opening and closing of garage doors at the soundof horns, to throw power switches upon detection of malfunctioning ofindustrial machinery, and the like.

The accompanying drawing illustrates one specific, convenient andeconomical mode for applying the concept and principles underlying ourinvention, special reference being had to a contraphase amplifier stage.

A contraphase amplifier is a descriptive term herein adopted forconvenience of expression. It is used herein to denote a conventionalelectron tube functioning to divide an inserted A.-F. spectrum into anupper-frequency and a lower-frequency band, respectively, said divisionbeing a function of partialdegenerative currentfeedback. From saidcontraphase amplifier 1, two outputs in opposite phase are taken, fromits cathode and plate, respectively, in a form of phase-splitter, saidoutputs being utilized to produce. contrary action in supplementalcircuitry. The contraphase. amplifier differs from a conventionalparaphase amplifier in that its respective outputs are neither ofidentical frequency-composition, symmetrical phase-relationship, nornecessarily of equal amplitude, as will be more fully disclosed, post.

The A.-F. signal representing the incoming program material is insertedinto the circuitry of our invention between grid-and groundofcontraphase amplifier tube 1.

A preliminary stage of voltage amplification may in some cases benecessary. The load on contraphase tube 1 is divided between plate loadresistor 2 and cathode resistor 4. Cathode resistor 4 is shunted withcathode bypass capacitor 5, the latter being inordinately small in valueas compared with normal design values in this application. Its precisevalue is selected with reference to associated'design values so thatfrequencies above approximately 400 C. P. S. are adequately bypassed inthe cathode circuit. Inverse feedback is therefore obtained as to theunbypassed frequencies, degeneration being confined to the band below400 C. P. S. A signal variation on the grid of tube 1 produces aplate-current variation through cathode resistor 4, but only in responseto signals falling within the lower-frequency band, below 400 C. P. S.Said plate-current variation follows the grid, thereby reducing theeffectiveness of the input signal in said lower-frequency band. Dualpurposes are thereby served. By selecting appropriate amplitudereference-levels, the output across partially-bypassed cathode resistor4 is limited to a lower-frequency band, below 400 C. P. S.; and, theplate output of tube 1 is limited to the complementary upper-frequencyband of the inserted signal spectrum, above 400 C. P. S.

Contraphase tube 1 may be any general purpose triode with an indirectlyheated cathode, but preferably a highmu triode with hightransconductance. Appropriate modifications may be made in its cathodecircuit, if necessary, either to increase or decrease its operating biasvoltage. Unlike the case of a paraphase amplifier, wherein identicalfrequency-composition of the respective outputs is important forpush-pull operation, no consideration need be given to the capacitancebetween the filament and cathode of contraphase tube 1.

As suggested, the fequency-division between the two outputs ofcontraphase tube 1 is made at approximately 400 C. P. S., which closelycorresponds to middle A-fiat on the musical scale. 50% of speech energyis developed by frequencies in the band below 400 C. I. S. Cathodebypass capacitor 5 is selected just small enough in value to confinedegeneration to the band below 400 C. P. S. To aid the sharpness of thisfrequency-division, plate coupling capacitor 3 is selected small enoughin value to offer high reactance to frequencies below 400 C. P. S.Cathode coupling capacitor 6 is made large enough in value to readilypass frequencies down toward the bottom of the energy-producing range ofspeech, to about 150 C. P. 8., yet not so low as to allow musical bassnotes to produce appreciable output from the quasicathode follower oftube 1.

The respective A.-F. outputs from the cathode and plate of tube 1 areopposite in phase and, as the drawing indicates, appear across resistors7 and 8, respectively. Said resistances 7 and 8 may be represented bythe complementary sections of one potentiometer, in practice, tofacilitate adjustment of the relative impedances in the diode circuitsof rectifiers 10 and 11, respectively.

Each output of tube 1 is rectified to a pulsating D.-C. voltage; theplate output, representing the energy produced by signals in theupper-frequency band, being rectified by diode 10 to a negative D.-C.voltage which appears across common load 9; the cathode-follower output,representing the energy produced by signals of the lower-frequency bandof the same inserted spectrum, being simultaneously rectified by diode11 to produce an opposing positive D.-C. potential across common load 9.

While the drawing shows the net effective resultant of the two D.-C.voltage components as a single resultant D.-C. control voltage acrosscommon load 9, (for eventual application to the grid of a relay-controltube or similar device), said dual. D.-C. voltage components may beindependently preserved, in any combination of polarities, for separateapplication to equivalent control circuitry. The latter may include thedriving of two independent relay-control tube grids; or the impressionof one D.-C. voltage on a control grid, while introducing the otherD.-C. voltage into cathode circuitry to have opposing effect on thebiasing of the same tube; or other means for producing from the twoD.-C. voltage components a similar net effective result.

With reference to the specific circuit of the drawing, the resultantD.-C. voltage across common load 9, after rectification, may be eitherpositive or negative in polarity, depending upon the relative magnitudesof the two rectified component voltages forming across said common load9. The latter voltages, in turn, are dependent upon the relativeamplitudes of the A.-F. signal voltages across resistances 7 and 8,respectively. Since the last-mentioned resistances may actually be thecomplementary portions of the same potentiometer in practice, therelative amplitudes of the two A.-F. signal voltages which supplyrectifiers 10 and 11 may be controlled by setting such potentiometers7-8. Such arrangement, consequently, also would provide a convenientmeans for controlling the relative magnitudes of the two rectifiedcomponents across common load 9.

The net resultant -D.-C. control voltage thus developed across commonload 9 is effective in the present applica tion (i. e., to discriminatebetween inserted speech and music signals, respectively), because of thelower upperfrequency to lower-frequency ratio of energy in speechsignals than in music signals, as hereinbefore detailed. Because of thisdifferential in energy-ratios, speech provides greater cancellation ofits own negative D.-C. component across common load 9 than does music.In fact, when said ratio falls below unity, as it does in the case ofspeech signals only, the net resultant D.-C. control voltage is actuallypositive. Music signals, on the contrary, develop across common load 9 aresultant D.-C. voltage negative in polarity, and greater in magnitudethan speech signals are capable of there developing in the negativedirection.

Though the use of a single contraphase amplifier stage 1 for producingboth of the split-frequency band outputs, aforementioned, is attractivefrom the standpoints of design-simplicity and construction-economy, itsuse necessarily cooperates with the remainder of the circuitry of ourinvention in its development of a definitive discriminating controlvoltage. The reason resides in phase differences concomitant tosplitting a frequency spectrum through the medium of a single electrontube, as in the manner hereinbefore disclosed. In the case of insertedspeech signals, the plate (upper-frequency band) output of contraphasetube 1, which ultimately produces a negative D.-C. voltage componentacross common load 9, (and which should be kept to a minimum duringspeech signals for effective discrimination), is almost exclusivelyproduced by harmonics. Speech harmonics, therefore, are out of phasewith their fundamentals, since the latter lie within the range of thecathode-follower (lowerfrequency) output. On the other hand, thefundamentals of a high proportion of music signals fall, along withtheir harmonics, within the upper-frequency band (above middle A-fiat,for example), which yields the plate output of tube 1. Said musicfundamentals are consequently in phase with the harmonics they produce.The advantage in having speech harmonics be 180 out of phase with theirfundamentals, while a high percentage of music harmonics are in phasewith their fundamentals, may be gathered from the following data.

During the positive half-cycle of a speech fundamental, its harmonicscontribute nothing to the magnitude of the negative D.-C. componentacross common load 9. During its negative half-cycle, even harmonicsdevelop some magnitude of negative component during 50% of thetime-duration of said fundamental tone, but the odd harmonics contributeto said negative component only 33-40% of the time-duration of thefundamental. On the other hand, that high proportion of musicfundamentals which produce harmonics in phase with themselves,

both forming part of the plate (upper-frequency) output of contraphasetube 1, contribute more generously to the magnitude of the negativeD.-C. voltage component across common load 9. For example, a negativeD.-C. voltage component is being fed to common load 9 during 100% of thenegative half-cycle of a music fundamental lying within theupper-frequency range, with the harmonic voltage content being additive50-67% of that time for all orders of harmonics. Thus, thephase-opposition between the cathode and plate outputs of contraphasetube 1, respectively, redounds to the advantage of music signals intheir mission of developing a higher magnitude of negative D.-C. controlvoltage across common load 9 than speech signals are able to theredevelop.

The net eifective resultant of the respective outputs of the two diodes10 and 11, which is shown in the circuitry of the drawing as a singleresultant D.-C. voltage across common load 9, and which discriminatesbetween inserted speech and music signals, respectively, may be appliedin various ways to control the acoustical output of the associatedequipment accordingly. One means for accomplishing this is shown in thedrawing, wherein said resultant D.-C. control voltage is applied todrive grid 16a of relay-control tube 16. Instead of applying saidcontrol voltage directly to grid 16a, an RC network 121314 is interposedbetween said grid 16a and common load 9. The latter network is,basically, anordinary series time-delay comprised of resistor 13 andcapacitor 14. Said delay network enhances the efiiciency of operation ofour circuit in that it serves to dampen the relatively highinstantaneous peak voltages developed in the upper-frequency range byspeech signals upon occasion, especially upon over-emphasis of words,throat-clearing, and the like. The RC constant of network 1314 might, inpractice, be of the order of 500-1000 millielement 13. Capacitor 12 isselected of such value as to offer high reactance to D.-C. pulsations inthe effective energy-producing speech range, or up to approximately 3000C. P. S.; and to offer progressively lower reactance to D.-C. pulsationsof higher frequencies, which latter are produced exclusively by musicsignals. Thus, time-delay network 13-14 is fully operative in thecircuit of our invention for all frequencies up through the effectiveenergyproducing speech range, but becomes progressively less elfectivein impeding pulsations of higher frequencies. Therefore, a single flutenote, for example, even though of very short duration, may quicklydevelop a negative D.-C. pulse on grid 16a of relay control tube 16,thus aiding to a more material degree other musicsignals in theirfunction of blocking said tube 16.

Capacitor 12, further, has a grid-leak biasing effect, when theresultant D.-C. voltage across common load 9 is positive in polarity,since current then flows in the grid circuit of relay-controltube 16.Through the greatly diminished cathode-to-grid resistance of tube 16,atsuch times, capacitor 12 quickly charges up to essentially the fullvalue of said positive control voltage and results in grid 16a, which isconnected to the low potential plat of capacitor 12, being heldessentially at cathode potential. This grid-leak action limits thepositive swing of control grid 16a, thereby adding to the life of tube16. The attendant reduction in effectiveness of a positive D.-C. controlvoltage on grid 16a is of negligible importance to the desired operationof our circuit.

Therefore, the resultant D.-C. control voltage which is developed acrosscommon load 9, and which-discriminates between speech and music,respectively, is applied 6 through variable delay network 1213l4 to grid16a of relay-control tube .16. Control .tube 16 is so biased by thepotential developed across its cathode resistor 15 (which may inpractice be made variable for convenience in adjustment) that the platecurrent through said tube 16, in the quiescent state, is just sufficientto .energize relay coil 17, thereby opening relay switch 17a. The latteraction opens voice coil circuit line 18, or more practically, as shownin the drawing, introduces into voice coil circuit line 18 apower-absorbing impedance 19. Before any inserted A.-F. signal canthereafter become audible, switch'17a must again be closed, therebyagain shorting out impedance 19. To accomplish this, a certain magnitudeof negative D.-C. voltage is required to be impressed upon grid 16a ofrelay-control tube 16, to so alter its bias that the plate currentthrough said tube 16 is reduced to the point where relay solenoid 17 isagain deenergized, thereby returning switch 17a to its normally-closedposition. Said D.-C. control voltage for impression upon grid 16a isdeveloped in the circuitry of our invention across common load 9, ashereinbefore detailed.

Upon the insertion into our circuitry of A.-F. signals comprised ofspeech, the control voltage developed across common load 9 is positivein-polarity; or, when negative, it fails to attain such magnitude that,when applied to grid 16a of relay-control tube '16, the latters platecurrent would be sufficiently reduced to deenergize relay coil.17.Therefore, upon speech signals, the quiescent state persists, in whichvoice coil circuit linelS remains impeded, said speech signals beingtherefore inaudible.

On the contrary, inserted music signals develop a negative D.-C. controlvoltage across common load 9 of our circuitry, said negative D.-C.control voltage being sulficient in magnitude that, when impressed upongrid 16a of relay-control tube 16, it decreases the latters platecurrent sufiiciently to deenergize relay coil 17, thereby returningswitch 17a to its normally-closed position. The latter action shuntsabnormal impedance 19, which restores the voice coil circuit line 18 toits normal condition, thus permitting the energization of the voice coilby said inserted music signals.

Circuit refinements may of course be made, according to the collateralobjects desired to be accomplished by our invention, or to elaborateupon the simple circuit as shown in the drawing for increased operatingefficiency. Some brief examples follow.

To limit the loss of upper-frequency energy into the circuit of lowerdiode 11, the latter may be isolated from the circuitry of diode 10 bythe insertion of an inductance between point 9a and the cathode ofrectifier 11, reference being had to the accompanying drawing. The addedchoke should have a low D.-C. resistance, and should offer highinductive reactance to the pulsating D.-C. output of diode 10.

A capacitor may be added in shunt with resistor 7 to aid in theappropriate frequency-division of inserted program material into anupper-frequency and a lower-frequency band, respectively.

A normally-open relay switch may be substituted for normally-closedswitch 17a shown in the drawing. Thereby music may be expunged frombroadcast programs, while speech signals alone are reproduced. Or, byemployment of a spdt switch in that position, a manually-operated toggleswitch may be provided on the control panel of our device for selectingone mode of operation or the other, depending upon whether thenormally-open or the normally-closed side of said spdt relay switch isthereby cut into the voice coil circuit line 18.

Further, a multiplicity of switches may be added to the relay to performsuch functions as feeding one type of signal to a monitor speaker orsecondary line of speakers, while the other type of signal is made toenergize a network of principal speakers; or, to shunt the secondarywinding of the associated audio output transformer 20 7 with a dummyresistive load in substitution for the associated voice coil when thelatter is disconnected, for the better protection of said transformer20; etc.

A vacuum tube relay circuit, or other completely electronic circuit, maybe arranged in substitution for the mechanical relay device shown in thecircuit of the accompanying drawing.

The power-absorbing impedance 19 may be made variable, for manuallypre-setting the degree of suppression of the program material deemed tobe of secondary importance in the particular application, whether saidmaterial be speech or music.

Other circuit refinements and adaptations will suggest themselves todesigners of electronic equipment. The textual matter of the abovedisclosure is presented in elucidation of our basic conception, andnothing therein is intended as a specific limitation on the practicalapplication thereof.

We claim:

I. Adjunctive to an associated system including a radio receiver orother signal device responsive to A.-F. signals with an audio amplifierand sound-reproducer, a selective electronic circuit connected to saidamplifier through means limiting the peak energy of received signals,including means for establishing a reference-frequency, means fordividing the A.-F. content of a received signal about saidreference-frequency effectively into a higherfrequency band and alower-frequency band relative to said reference-frequency, means foraveraging the respective energy-contents of said respectivefrequencybands, means for distinguishing between respective signalswhose average energy lies preponderately in said higher-frequency bandand preponderately in said lowerfrequency band, with further means forpermitting or impeding the activation of the associated sound-reproducerby said received signal according to the type of signal as hereinbeforedistinguished by said adjunctive circuit.

2. Adjunctive to an associated system including a radio receiver orother signal device responsive to A.-F. signals with an audio amplifierand sound-reproducer, a selective electronic circuit connected to saidamplifier through means limiting the peak energy of received signals,including means for establishing a reference-frequency, means fordividing the A.-F. content of a received signal about saidreference-frequency effectively into a higher-frequency band and alower-frequency band relative to said reference-frequency, means forindependently rectifying the energy of said respective frequency-bandsinto D.-C. voltages of mutually-opposing polarities, means for composingsaid respective D.-C. voltages into one resultant D.-C. control voltagebearing the polarity of its dominant D.-C. voltage component andequalling in magnitude the absolute voltage-differential existingbetween said respective component voltages, means operative uponexcitation by a predetermined minimum value of said absolutevoltage-differential of that polarity developed by the energy of saidhigher-frequency band, and a relay connected to the last mentionedmeans, said relay operating to select between activation and suppressionof said associated sound-reproducer upon operation of said lastmentioned means.

3. Adjunctive to an associated system including a radio receiver orother signal device responsive to music and speech signals with an audioamplifier and sound-reproducer, a selective electronic circuitdiscriminatory between received music and speech signals connected tosaid amplifier through means limiting the peak energy of receivedsignals, including means for dividing the A.-F. content of a receivedsignal comprising music or speech about a preselectedreference-frequency effectively into a higher-frequency band and alower-frequency band relative to said reference-frequency, means foraveraging the respective energy-contents of said frequency-bands, meansfor establishing said reference-frequency at such appropriate frequencythat the average energy of representative music signals fallspredominantly in said higherfrequency band while conversely the averageenergy of representative speech signals falls predominantly in saidlower-frequency band, means for distinguishing between respectivereceived signals whose average energy lies preponderately in saidhigher-frequency band, as in music signals, and preponderately in saidlower-frequency band, as in speech signals, with further means forpermitting or impeding the activation of the associated sound-reproducerby the received signal according to whether said electronic circuit thusdetermines said signal to be music or speech, respectively.

4. A selective electronic circuit excited by a signal inserted from anexternal source through means limiting the peak energy of said signal,with means for establish ing a reference-frequency, means for dividingthe frequency-content of said inserted signal about saidreference-frequency effectively into a higher-frequency band and alower-frequency band relative to said referencefrequency, means forindependently rectifying and averaging the respective energy-contents ofsaid frequencybands into D.-C. voltages of mutually-opposing polarities,means for composing said respective D.-C. voltages into one resultantDC. control voltage bearing the polarity of its dominant D.-C. voltagecomponent and equalling in magnitude the absolute voltage-ditferentialexisting between said respective component D.-C. voltages, and means forapplying said resultant D.-C. control voltage to control the operationof a relay according to the polarity and magnitude of said resultantvoltage.

5. A selective electronic circuit excited by a signal inserted from anexternal source through means for limiting the peak energy of saidsignal, with means for establishing a reference-frequency, means fordividing the frequency-content of said inserted signal about saidreference-frequency effectively into a higher-frequency band and alower-frequency band relative to said reference-frequency, means forindependently rectifying and averaging the respective energy-contents ofsaid frequencybands into D.-C. voltages of mutually-opposing polarities,and means for applying said respective D.-C. voltages in combination tocontrol the operation of a mechanism according to the respectivepolarities and magnitudes of said D.-C. voltages.

6. Adjunctive to an associated system including a radio receiver orother signal device responsive to music and speech signals with an audioamplifier and sound-reproducer, a selective electronic circuit connectedto said amplifier through means limiting the peak energy of receivedsignals, including means for dividing a received A.-F. spectrumcomprising music or speech about a preselected reference-frequencyeffectively into a higherfrequency band a lower-frequency band relativeto said reference-frequency, means for independently rectifying theenergy of said respective frequency-bands into D.-C. voltages ofmutually-opposing polarities, means for composing and averaging saidrespective D.-C. voltages into one resultant D.-C. control voltagebearing the polarity of that aforesaid component voltage dominant inaverage energy, means for establishing said reference-frequency at suchappropriate frequency that, relative thereto, said division of musicsignals alone can produce a ratio of higher-frequency to lower-frequencyaverage energy exceeding unity and a consequent resulting D.-C. controlvoltage opposite in polarity to that resulting from a correspondingdivision of speech signals, said electronic circuit including furthermeans for applying said resultant D.-C. control voltage to control theoperation of a relay according to the polarity of said resultant D.-C.control voltage, said relay correspondingly controlling the acousticoutput of said associated sound-reproducer.

7. Adjunctiveto an associated system including a radio receiver or othersignal device responsive to music and speech signals With an audioamplifier and sound-reproducer, a selective electronic circuit connectedto said amplifier through means limiting the peak energy of re ceivedsignals, including means for dividing a received A.F. spectrumcomprising music or speech about a preselected reference-frequencyeffectively into a higherfrequency band and a lower-frequency bandrelative to said reference-frequency, means for independently rectifyingthe energy-contents of said respective frequencybands into D.-C.voltages of mutually-opposing polarities, means for composing andaveraging said respective D.-C. voltages into one resultant D.-C.control voltage bearing the polarity of that aforesaid component D.-C.voltage dominant in average energy and equalling in magnitude theabsolute voltage-differential existing between said respective componentD.-C. voltages, means for establishing said reference-frequency at suchappropriate frequency that, relative thereto, said division of musicsignals produces a ratio of higher-frequency to lower-frequency averageenergy sufficiently greater than that producible by a correspondingdivision of speech signals to consequently develop in the polarity ofsaid rectified higherfrequency energy a resultant D.-C. control voltageof a magnitude unattainable by speech signals, said electronic circuitincluding further means for applying said resultant D.-C. controlvoltage to control the operation of a relay according to the magnitudeand polarity of said resultant voltage, said relay correspondinglycontrolling the acoustic output of said associated soundreproducer.

8. Adjunctive to an associated system including a radio receiver orother signal device responsive to A.-F. signals with an audio amplifierand sound-reproducer, a selective electronic circuit including acathode-biased electron tube with a received A.-F. spectrum collaterallyimpressed on its grid by the said associated amplifier through meanslimiting the peak energy of received signals, with loading means forrealizing a dual output respectively from the plate and cathode of saidelectron tube, means for establishing a reference-frequency, means fordegenerating in the plate output of said electron tube audio frequenciesbelow said reference frequency, means for degenerating in the cathodeoutput of said electron tubeaudio frequencies above saidreference-frequency, means for independently rectifying the energy ofsaid respective outputs of said electron tube into D.-C. voltages ofmutually-opposing polarities, means for composing and averaging saidrespective D.- C. voltages into one resultant D.-C. control voltagebearing the polarity of its dominant DC. voltage component and equallingin magnitude the absolute voltage-differential existing between saidrespective component D.-C. voltages, and means for applying saidresultant D.-C. control voltage to control the operation of a relayaccording to the polarity and magnitude of said resultant controlvoltage, said relay correspondingly controlling the acoustic output ofsaid associated soundreproducer.

9. In an electronic circuit with means for dividing thefrequency-content of an inserted signal about a predeterminedreference-frequency into a higher-frequency band 60 and alower-frequency band relative to said referencefrequency, with means forindependently rectifying and averaging the respective energy-contents ofsaid frequencybands, and with means for controlling a mechanismaccording to the resulting ratio of average higher-frequency energy tolower-frequency energy, manually-operated means for variably regulatingsaid ratio producible from a given inserted signal, said latter meansoperating to 10 vary the relative impedance in said respectiverectifying circuits.

10. In an electronic circuit with means operating to control a mechanismaccording to the distribution of the total energy of an inserted signalfrequency-spectrum respectively between its higher-frequencies and itslowerfrequencies relative to a predetermined reference-fire quency,means for dividing the energy of said inserted frequency-spectrum aboutsaid reference-frequency, said latter means including a cathode-biasedelectron tube with said inserted signal impressed on its grid, acapacitor shunting the cathode-biasing resistor of said electron tube,said capacitor being of such inordinately small capacitance to producedegenerative current feedback in the stage of said electron tube as tosaid lower-frequencies of the inserted signal but not sufiiciently smallin capacitance to prevent ad-equate frequency-bypassing of saidhigher-frequencies of said signal, means for developing in the platecircuit of said electron tube from the undegenerated higher-frequenciesof an inserted signal an output substantially equal in energy to anoutput simultaneously developed in the cathode circuit of said tube fromthe inadequately-bypassed lower-frequencies of the same inserted signalwhen said signal is at said reference-frequency, means coupling saidplate output to its load offering progressively less impedance tofrequencies above said reference-frequency, and means coupling saidcathode output to its load offering progressively less impedance tofrequencies below reference.

11. Means for dividing the contents of a frequencyspectrum about apredetermined reference-frequency cf fectively into two bandscomplementary in frequencycontent, said bands respectively comprising ahigherfrequency band and a lower-frequency band relative to saidreference-frequency, said means including a cathodebiased electron tube,means for dividing the load on said tube between its plate and cathodecircuitry to produce substantially equal loading on each said respectivecircuit upon impression on the grid of said electron tube of a signal atsaid reference-frequency, a network in the cathode circuit of said tubeof such component values as to be progressively more discriminatoryagainst frequencies higher than said reference-frequency and operativeto produce progressively increasing degenerative current feedback in thestage of said tube upon impression of signals at frequencies below saidreference-frequency, said cathode network being further operative tovariably bias said tube according to the frequency of the impressedsignal, loading means for realizing an output from the plate of saidtube comprising the undegenerated frequencies of said higher-frequencyband, loading means for realizing an output from the cathode circuit ofsaid tube comprising the frequencies of said lower-frequency bandinadequately bypassed in said cathode network, means coupling said plateoutput to its said loading means progressively more discriminatoryagainst frequencies below reference, "and means coupling said cathodeoutput to its said loading means progressively more discriminatoryagainst frequencies above reference.

References Cited in the file of this patent UNITED STATES PATENTS Re.21,151 Adair July 18, 1939 2,089,637 Adair Aug. 10, 1937 2,250,596Mountjoy July 29, 1941 2,424,216 Atkins July 22, 1947 2,575,109 HowesNov. 13, 1951

